Electric explosive initiator



Oct. 3, 1961 J. w. HAAS 3,002,458

ELECTRIC EXPLOSIVE INITIATOR Filed Dec. 29, 1955 Fi g1 JohnwHaasINVENTOR.

ATTORNEXS This invention relates to an improved electrical explosiveinitiator of the type commonly used, for example, in ordnance devices.In initiators of known construction, it is common to provide electricalmeans for igniting an initiating explosive which, in turn, then ignitesand causes explosion of the main charge, either directly or through adelay charge. However, due to the many variable factors involved inmanufacturing and assembling such devices there is usually a rather Widevariation among individual initiators with the result that in certaincases an occasional initiator of a particular design will be fired whensay only 10 volts is applied to its firing terminals whereas other ofthe same design will not fire until some considerably higher voltage,say, 50 volts, is applied. While most such devices will not fire untilthe higher voltage is approached, the fact that an occasional one mightfire at a relatively low voltage, greatly increases the danger involvedin the manufacture of such devices and severely limits the testing ofthe devices or their associated fin'ng circuits.

It is an object of this invention to provide an improved electricalexplosive initiator of the type under consideration wherein firing ofthe initiator at a voltage below a pre determined minimum voltage willbe prevented.

A further object is to provide such an initiator construction wherein,without requiring unduly painstaking manufacturing procedures, the rangeof voltage between that voltage which can safely be applied withoutcausing firing of any of the initiators, and that voltage which must beapplied to insure that all initiators will be fired, is relativelysmall.

A further object of this invention is to incorporate in an initiator ofthe type under consideration, a high resistance material in series withthe electrical igniter normally incorporated therein, which materialwill limit current flow to a value too low to permit firing of anyinitiator until application of a voltage sufliciently high to insurefiring of all initiators, whereupon it will change from its highresistance condition to a condition wherein it afiords a relatively lowresistance path, thereby enabling sufiicient current to pass through theigniter to fire the charge.

Further and other objects will become apparent from the followingdescription and claim especially when considered in the light of theaccompanying drawing wherein:

FIG. 1 is a sectional view showing the invention applie to an initiatorof known type;

FIGS. 2 and 3 are sectional views showing the invention applied toinitiators of somewhat difierent type from that shown in FIG. 1.

The initiator shown in FIG. 1 is primarily of known construction andcomprises a main cup or casing 1 containing, near its lower end, anexplosive charge 2. Directly above the explosive charge 2 is an ignitioncharge 3 which is confined within a sleeve 4. Immediately above thesleeve 4 is a body or plug of insulating material 5 which is providedwith a pair of generally cylindrical bores or recesses 6, extendingdownwardly from the upper end thereof. These recesses are filled with afusible, homogeneous mixture 7 of a wax or wax-like dielectric materialheavily impregnated with very fine particles 15 of metal, such asaluminum dust or flour. Covering the open end of the casing, is a capmember 9 of insulating material, the casing wall being crimped over thecap member, as clearly EfifiZASS Patented Oct. 3, I961 ice '11 ofconductors 10 are the upper ends 12 of a second pair of conductors 13,the lower ends of which are bridged by an igniter 14.

The mixture 7 in the recesses 6 may be formed of substantially equalparts by weight of aluminum dust or flour and some such wax as aceresine wax. Instead of a wax, other relatively low-temperature fusibledielectric materials, such as some of the commercially availablesilicones may be substituted. Thus, for example, thesilicones,commercially available from the Dow-Corning Corporation, and designatedas DC996 or 997, are suitable for such use. While the ratio of metal todielectric material may by varied somewhat from the 1:1 ratio mentionedabove, the tllescribed ratio has been found to give very consistentI'BSII IS.

FIG. 2 sl ws a somewhat difierent type of initiator 7' which, instead ofusing a bridge type igniter as in FIG. 1, makes use of an ignitioncharge 16 which is itself electrically conductive. In this embodimentthe recess 17, containing the dielectric-metal mixture, is formed in thecap member 18 rather than in the plug 19. Moreover, but a singleterminal conductor 20 is utilized, the casing 21 itself serving as theother side of the electrical firing circuit. Ignition is produced by theflow of current from the lower conductor 22 through the ignitionexplosive 16 to the casing 21.

FIG. 3 shows an initiator very similar to that illustrated in FIG. 1 butwhich utilizes a conductive mixture 23 as the ignition explosive. Inthis case, as in FIG. 1, two separate electrical input conductors 24 areutilized, ignition being obtained as a. result of the flow of currentthrough the ignition charge 23 between the lower conductors 25.

The dielectric-metal mixture utilized in the initiators has very highresistance characteristics under low voltage conditions and will limitcurrent flow through the ignitor to a safe, extremely low valueuntil theapplied voltage is raised to a predetermined higher value, at which timethe mixture suddenly breaks down to a very low resistance value. Theexact voltage value at which such breakdown occurs will depend, ofcourse, upon the spacing between the ends of the conductors 10 and 12(FIG. 1) and upon the particular composition of the mixture utilized.Representative resistance values from conductor 10 to conductor 12 foran initiator constructed as in FIG. 1 will be well over 100,000 megohmsprior to breakdown, and only 2 to 10 ohms after the breakdown voltage ofabout 50 volts has been reached. Breakdown occurs so rapidly when thepredetermined voltage is reached that no undesired time delay isintroduced thereby. While, of course, there will be some variation inthe value of the voltage required to break down the material, in anyparticular initiator design the range of voltages between that at whichnone of the initiators will be fired and that which will insure that allsuch initiators will be fired, will be relatively small. With aninitiator of the type described there is therefore no danger ofaccidental firing of the initiator so long as any test voltages whichmight be applied thereto are held a few volts below the lower limit ofthis range.

The operation of the initiator is believed obvious. When it is desiredto cause firing thereof, a voltage slightly above the breakdown voltageis applied to the outer ends of conductors 10, causing breakdown of theimpregnated dielectric mixture 7 in the recesses 6, which thereuponpermit suflicient current to flow through the ignitor bridge 14, tocause it to ignite the ignition charge 3 which in turn ignites theexplosive charge 2.

While the invention has been illustrated in conjunction with but threespecific initiator constructions, it is believed obvious that it isequally applicable toothcr types of initia. tors and that many changesmay be made without departing from the spirit and scope of the inventionas defined by the appended claim.

I claim:

In an electric explosive initiator having a generally cylindrical casingopen at its one end, explosive material and electrically controlledignition means therefor canied Within said casing, a plug of insulatingmaterial closely fitted within said casing between said explosivematerial and said open end, said plug being provided with a pair oflaterally spaced, generally cylindrical recesses opening toward saidopen end and extending inwardly part way through said plug, a first pairof conductors ex-tending outwardly through said plug from saidignition'means into the inner closed ends of said recesses respectively,a cap member of insulating material fitted within and closing the openend of said casing and covering the open ends 4 p of said recesses; saidcap member being provided with a second pair of conductors, extendingtherethrough, the inner ends of said second conductors extending intosaid open ends of said recesses in substantial axial alignment with theends of said first conductors but spaced axially therefrom, and a massof readilyiuslble dielectric material heavily impregnated with finelydivided metallic particles which are dispersed throughout saiddielectric material filling each of said recesses the ends of theconductors in each recess being embedded in said mass whereby the latterelectrically bridges the gap between said conductors.

References Cited in the file of this patent UNITED STATES PATENTS2,658,451 Home Nov. 10,- 1953 FOREIGN PATENTS 611,915 Germany Apr. 9,1935

